1. Field of the Invention
The present invention relates to a magnetic recording medium and a magnetic recording and reproducing apparatus, and more particularly relates to a magnetic recording and reproducing apparatus excellent in achieving higher recording density and higher reliability.
2. Description of the Related Art
A magnetic disk apparatus used as an external storage unit for a large-sized computer or a personal computer system has been demanded to increase a recording capacity (areal density) per disk. In order to achieve a higher recording density, it will be required in the future to reduce a magnetic spacing from a reader and writer in a magnetic head to a magnetic layer and to improve recording and reproduction performance, positioning accuracy, and reproduction signal processing performance with respect to the magnetic head and a magnetic recording medium. Particularly, since magnetic field strength is in inverse proportion to the magnetic spacing squared, the areal density is significantly increased when the magnetic spacing is reduced. The magnetic spacing is expressed as a sum of a flying height at a position of the reader and writer in the magnetic head stably flying above a surface of the magnetic recording medium on the basis of principles of air film lubrication, a dent caused by a difference in a processing amount of a magneto-resistive sensor exposed part in a magneto-resistance effect type magnetic head, a slider overcoat thickness, a medium lubrication film thickness and a medium overcoat thickness. The magnetic spacing is reduced by reducing values of those described above. When the flying height at the position of the reader and writer in the magnetic head is reduced to several nm, the following problems occur. Specifically, the slider is likely to intermittently come into contact with rough protrusions on a disk surface. Moreover, when the protrusions are reduced in size to smooth the disk surface, contact vibration is caused by a meniscus adsorptive force of the lubrication film.
In recent years, a discrete track magnetic recording system and a bit patterned magnetic recording system have been proposed as innovative technologies to respond to the higher recording density of the magnetic disk apparatus. These are technologies that allow higher track density and higher recording density by forming grooves between recording tracks in a magnetic recording medium or by isolating bits to reduce magnetic interference between the adjacent tracks or the bits. In a magnetic recording medium described in Japanese Patent Application Laid-Open Publication No. 2005-108335, a film surface on a cross-section passing a center of a ferromagnetic dot of a carbon film that is a medium overcoat has a smooth shape which is gradually reduced toward outside from the center. Specifically, a thickness of the carbon film is not uniform and there is film thickness distribution. Moreover, a thickness of a center portion passing the center of the ferromagnetic dot is 5 nm, and the thickness of the carbon film at a position of 1/10 of a radius of the ferromagnetic dot from an end portion is 3.5 μm. The carbon film having such a cross-sectional shape is formed by performing etching in which an ion incident angle is gradually changed from a substrate perpendicular direction to a longitudinal direction. In an information recording medium described in Japanese Patent Application Laid-Open Publication No. 2005-276325, a non-magnetic material is buried in respective concave portions of a magnetic layer formed into a predetermined concave-convex pattern, and a non-magnetic layer is formed on respective convex portions of the magnetic layer. Moreover, an upper center of each of the convex portions of the magnetic layer is formed into an angular shape gradually protruding upward. A protrusion amount thereof is 1 nm. Such a shape is formed by setting a long ion beam etching time for the non-magnetic layer. A nanostructure described in Japanese Patent Application Laid-Open Publication No. 2005-52956 includes a first columnar member and a second member formed so as to surround the first member. The second member contains two kinds or more of materials that can form eutectic crystal. Moreover, one of the materials is a semiconductor material, a height of the first member from a substrate is higher than that of the second member from the substrate, and a protrusion of the first member has a conical shape.